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1Essential

Vitamin D3

Also sold as Cholecalciferol, vitamin D

Sun exposure is unreliable indoors, at latitude, and with darker skin. Levels fall back within weeks of stopping.

TrustedSupp Tier System™ · Tier 1Take persistently
Check before you startThis one has documented interactions with medication classes where the consequences are serious. If you take any prescription medicine, run it past a pharmacist before starting.

Evidence strength

92/100Very strong
WEAKLIMITEDMODERATESTRONGVERY STRONG

What the evidence supports: correcting deficiency and supporting bone health.

This scores how well-supported the claim above is — not how much benefit you personally would get. A high score on a narrow claim does not extend to everything the product is marketed for.

How long to take it

Ongoing. This is a structural gap, not a phase — most people take it for life, ideally with a blood level checked yearly.

Who it's actually for

Almost everyone at northern latitudes, anyone mostly indoors, darker skin tones, older adults, and those who cover up.

Safe upper limit

Verified
100 mcg / 4,000 IU per day
Fat-soluble and stored. Sustained excess raises blood calcium, which can damage kidneys and calcify soft tissue.
Vitamin D — Health Professional Fact SheetChecked Fri Aug 14 2026 00:00:00 GMT+0000 (Coordinated Universal Time)
UL ranges 25–100 mcg (1,000–4,000 IU) by age; 100 mcg/4,000 IU is the adult figure.

Interactions to know about

Other supplements:

Run your full list through the interaction check.

Practical notes

  • Take with a meal containing fat — absorption roughly doubles.
  • Pair with K2 so the calcium it mobilises goes to bone, not arteries.
  • Weekly dosing works as well as daily if that's easier to remember.